Die Casting Mold and Improved Vent Structure Used Therein

ABSTRACT

A die casting mold includes a resistance member ( 17 ) disposed in a vent passage ( 16 ) to reduce a flow velocity of molten metal as the molten metal advances along the vent passage. The resistant member comprises a plurality of discrete protrusions ( 24 ) arranged in staggered relation to one another in both a longitudinal direction and a transverse direction of the vent passage so as to define therebetween a labyrinthine part ( 34 ) extending between an inlet side and an outlet side of the vent passage.

TECHNICAL FIELD

The present invention relates to an improvement in and relating to a die casting mold having a chill vent structure to allow for escape of air and/or gas from a die cavity while preventing a molten metal from being flashed outside of the die casting mold when charging the molten metal into the die cavity.

BACKGROUND ART

A die casting mold having a chill vent structure to allow for efficient exhausting of residual air and/or gas from a die cavity without causing flashing of unsolidified molten metal when a molten metal is forced under pressure into the die cavity is disclosed, for example, in Japanese Patent Laid-Open Publication (JP-A) No. 11-151564. The chill vent structure of the disclosed die casting mold will be described below with reference to FIG. 7.

As shown in FIG. 7, the chill vent structure includes a chill vent block 100 consisting of a pair of vent halves or members 102 and 104 fixed to a cooperating pair of die casting mold members 101 and 103, respectively. The vent members 102, 104 have confronting surfaces corrugated so as to define therebetween a vent passage 105 of zigzag shape when the mold members 101, 103 are brought together to close a die casting mold. The zigzag-shaped vent passage 105 is in communication with a die cavity 106 formed between the mold members 101, 103. With this arrangement, when a molten metal is forced under pressure into the die cavity 106, residual air and/or gas in the die cavity 106 is allowed to escape from the vent passage 105, followed by flashing of unsolidified molten metal from the die cavity 106 into the vent passage 105. In this instance, since the zigzag-shaped vent passage 105 provides a relatively long flow path, the flashing unsolidified molten metal is chilled by the vent members 102, 104 and becomes solidified within the vent passage 105. Thus, flashing or eruption of unsolidified molten metal from the die casting mold can be avoided.

However, since the chill vent block 100 is formed by a pair of vent halves or members 102, 104 fixed to the cooperating pair of mold members 101, 103, respectively, of the die casting mold, the overall size of the die casting mold is relatively large. Furthermore, the vent members 101, 103 having corrugated surfaces require a high-precision processing for the manufacture thereof, which will increase the production cost of the chill vent block 100. Additionally, the corrugated vent member surfaces tend to hinder smooth separation of a die cast article or casting from the mold members 101, 103 when the casting is to be removed from the die casting mold. Furthermore, when a depth t (FIG. 7) of the vent passage 105 or an apex angle θ (FIG. 7) of triangular ridges on the corrugated vent member surfaces is to be changed to adjust a flow velocity of molten metal as the molten metal advances along the vent passage 105, the vent members 102, 104 as a single chill block should be replaced with another pair of vent members of desired configuration. Such replacement of the pair of vent members involves high additional cost incurred.

In view of the foregoing difficulties of the conventional device, it is desirable to provide a die casting mold having a chill vent structure, which is relatively small in size, simple in construction and inexpensive to manufacture and, can be assembled with the die casting mold without increasing the overall size and cost of the die casting mold.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, there is provided a die casting mold comprising a fixed mold member, a movable mold member movable toward and away from the fixed mold member to define therebetween a die cavity when the die casting mold is closed, a vent passage formed in a mating surface of one of the fixed mold member and the movable mold member and extending in communication with the die cavity to allow for escape of residual air and/or gas from the die cavity when a molten metal is charged into the die cavity, and a resistance member disposed in the vent passage to reduce a flow velocity of the molten metal as the molten metal advances along the vent passage, wherein the resistant member comprises a plurality of discrete protrusions arranged in staggered relation to one another in both a longitudinal direction and a transverse direction of the vent passage so as to define therebetween a labyrinthine part extending between an inlet side and an outlet side of the vent passage.

With this arrangement, the resistance member is disposed in the vent passage formed in a mating surface of the fixed or movable mold member. This means that the resistance member is disposed inside the die casting and does not enlarge the overall size of the die casting mold. Furthermore, since the resistance member can be formed by machining only one mold member, the production cost of the die casting mold is relatively low as compared to the conventional die casting mold having a chill vent block formed by a pair of vent members fixed to a pair of mold members, respectively, of the die casting mold.

Preferably, a mating surface of the other of the fixed mold member and the movable mold member has a flat portion adapted for abutment with top surfaces of the protrusions. Since the flat mating surface portion is unlikely to stick to the material of a die cast article or casting, the casting can be readily removed from the die casting mold.

Preferably, the top surfaces of the protrusions are flat and engageable flatways with the flat mating surface portion of the other mold member. With this arrangement, when the mold is kept closed under a predetermined clamping pressure, the resistance member is held stably without casing deformation of the protrusions. Thus, during the die casing process, the cross-sectional area of the labyrinthine vent passage part remains substantially unchanged and gives no adverse effects on the qualities of die cast articles or castings.

The labyrinthine part of the vent passage includes a plurality of parallel spaced first grooves extending in the longitudinal direction of the vent passage and a plurality of parallel spaced second grooves extending in the transverse direction of the vent passage. The second grooves may be deeper than the first grooves so that a desired resistance can be obtained when the molten metal advances along the labyrinthine vent passage part.

In one preferred form of the invention, the resistance member is formed by a separate member structurally independent from the one mold member and removably mounted to the one mold member. The resistance member includes a flat plate-like base detachably mounted to the one mold member, and the protrusions are formed on one surface of the flat plate-like base.

Thus, by preparing two or more resistance members whose protrusions are different in number and size, it is possible to change the resistance members as appropriate according to desired qualities of a die cast article or casing to be produced. More specifically, since a flow velocity of molten metal as the molten metal advances along the vent passage is variable with the cross-sectional area of the vent passage, by changing the resistance members in an appropriate manner, it is readily possible to adjust the flow velocity of the molten metal at the resistance member to the extent that residual air and/or gas in the die cavity is fully exhausted without being dragged into the molten metal, which would otherwise result in gas holes and the like in the die cast article or casting, thereby degrading the product qualities of the casting. Thus, castings with desired qualities can be obtained without requiring a long time adjustment and preparation of the die casting mold.

Furthermore, by standardizing the size and shape of the bases of the respective resistance members as well as the size and shape of retaining recesses of the respective holders in which the resistance members are fitted, it is possible to use one resistance member in combination with plural different molds, or alternatively plural different resistance members can be used in combination with one mold. With this arrangement, the maintenance cost of the die casting mold can be reduced.

According to another aspect of the present invention, there is provided a chill vent structure for a die casting mold, comprising a flat plate-like base, and a plurality of discrete protrusions formed on one surface of the flat plate-like base and arranged in staggered relation to one another so as to define there-between a vent passage of labyrinthine structure.

By virtue of the labyrinthine structure, the vent passage can provide a relatively long flow path and a relatively large resistance to movement of molten metal as the molten metal advances along the vent passage. Thus, the molten passage, as it advances along the labyrinthine vent passage, is chilled and become solidified. Undesired flashing or eruption of unsolidified molten metal from the die casting mold can thus be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a vertical cross-sectional view showing a die casting mold according to an embodiment of the present invention;

FIG. 2 is an enlarged view of a portion of FIG. 1, which is indicated by a circle 2 shown in FIG. 1;

FIG. 3 is a schematic view in a direction of arrow 3 shown in FIG. 2;

FIG. 4 is a perspective view of a resistance member shown in FIG. 3;

FIG. 5 is a view similar to FIG. 3, but showing the manner in which residual air and/or gas in a die cavity is exhausted through a labyrinthine vent passage part formed in the resistance member;

FIGS. 6A, 6B, 6C and 6D are diagrammatical views showing a sequence of operations of a die casting process carried out on the die casting mold; and

FIG. 7 is a cross-sectional view showing a chill vent structure incorporated in a conventional die casting mold.

BEST MODE FOR CARRYING OUT THE INVENTION

Initial reference is made to FIG. 1 showing in cross section a die casting mold 10 embodying the present invention. The die casting mold 10 comprises a fixed mold member 11 and a movable mold member 12 movable toward and away from the fixed mold member 11 to define therebetween a die cavity 13 when the die casing mold 10 is dosed. The movable mold member 12 is mounted on a die holder 20 of a die cast machine. While the die casting mold 10 is kept in a closed state, a plunger 14 reciprocally movable within an injection cylinder 15 is driven to force a molten metal under pressure into the die cavity 13 to thereby form a die cast article or casting 39.

The fixed mold member 11 has a vent passage 16 formed in a mating surface 26 (FIG. 2) thereof. The vent passage 16 extends in communication with the die cavity 13 when the mold 10 is dosed. Thus, when charging molten metal into the die cavity 13, residual air and/or gas in the die cavity 13 is allowed to escape through the vent passage 16. A chill vent block (resistance member) 17 is disposed in the vent passage 16 to reduce a flow velocity of molten metal as the molten metal advances along the vent passage 16.

An exhaust valve 18 comprises a poppet valve incorporated in the fixed mold member 11 for opening and closing an outlet end of the vent passage 16. The poppet valve 18 has a stem 19 received in a valve hole 21 formed in the fixed mold member 11. The valve hole 21 has one end connected to the outlet end of the vent passage 16 and an opposite end closed by an actuator (not designated) of the exhaust valve 18. The valve hole 21 is connected to an inlet end of an exhaust passage 22 formed in the fixed mold member 11, an outlet end of the exhaust passage 22 being connected to an exhaust ventilation device (not shown) disposed outside the die casting mold 10.

With this arrangement, when a molten metal is forced under pressure into the die cavity 13 while the mold 10 is kept in the closed state, residual air and/or gas in the mold cavity 13 is discharged outside the mold 10 successively through the vent passage 16 including the chill vent block 17, the valve hole 21, and the exhaust passage 22. In this instance, the external exhaust ventilation device (not shown) is continuously driven, and on-off operation of the exhaust valve (poppet valve) 18 is adjustably controlled such that the exhaust valve 18 first opens the vent passage 16 to allow for escape of residual air and/or gas in the die cavity 13 and then closes the vent passage 16 until the molten metal is fully distributed within the die casting mold 10.

FIG. 2 shows in cross-section the resistance member 17 disposed in the vent passage 16 extending between the die cavity 13 and the valve hole 21. The resistance member 17 is detachably connected by screws 28 to a holder 27 fixedly mounted in the fixed mold member 11. Thus, the resistance member 17 is removably mounted to the fixed member 11.

The resistance member 17 includes a flat plate-like base 23 (see FIG. 4) and a plurality of discrete protrusions 24 formed integrally with and projecting from one surface of the base 23. The base 23 is fit in a retaining recess 35 formed in the holder 27. The protrusions 24 each have a flat top surface 25, which comes in face to face contact with a flat mating surface 26 of the movable mold member 12 when the mold 10 (FIG. 1) is closed. The protrusions 24 are disposed in the vent passage 16 so that the molten metal, as it advances along the vent passage 16, strikes the protrusions 24 and slows down advancing movement thereof. Thus, the protrusions 24 serve to interfere smooth advancing movement of the molten metal and hence reduces a flow velocity of the molten metal as the molten metal advances along the vent passage 16.

Since a portion of the mating surface 26 of the movable mold member 12, which comes in contact with the top surface 25 of the protrusions 24, is flat, a flashing part of the molten metal solidified inside the vent passage 16 is unlikely to stick to the mating surface portion of the movable mold member 12 when the die cast article 39 (FIG. 1) is removed from the mold 10. The die cast article 39 can thus be removed smoothly from the mold 10.

In the illustrated embodiment, the resistance member 17 is mounted in the fixed mold member 11 with the protrusions 24 disposed inside the vent passage 16 with their top surfaces 25 facing the movable mold member 12. As an alternative, the resistance member 17 may be mounted in the movable mold member 12. In the latter case, the movable mole member 12 has a vent passage formed in the mating surface 26 for receiving therein the protrusions 24 of the resistance member 14 with the top surface 25 facing the fixed mold member 11.

FIG. 3 shows the resistance member 17 as it is mounted to the holder 27 with the exhaust valve (poppet valve) 18 and the valve stem 19 omitted for clarity. The holder 27 is fixedly incorporated in the fixed mold member 11 so that a front surface of the holder 27 forms a part of the mating surface 26 of the fixed mold member 11 in which the vent passage 16 is formed. The vent passage 16 includes an inlet side portion 31, an outlet side portion 32L, 32R, 33L 33R and a central portion 34 disposed between the inlet side portion 31 and the outlet side portion 31L, 32R, 33L 33R. The inlet side portion 31 of the vent passage 16 is connected at one end (upstream end) to the die cavity 12 (FIG. 2) and at the other end (downstream end) to the central portion 34. The outlet side portion 32L, 32R, 33L 33R of the vent passage 16 includes a plurality (four in the illustrated embodiment) of longitudinal channels 32L, 32R connected at upstream ends to the central portion 34, and two transverse channels 33L, 33R interconnecting downstream ends of the longitudinal channels 32L, 32R and the valve hole 21. The central portion 34 of the vent passage 16 has a labyrinthine structure formed between the plural protrusions 24 arranged in staggered relation to one another in both a longitudinal direction and a transverse direction of the vent passage 16. The resistance member 17 forming the central portion 34 of the vent passage 16 has a two-piece structure including left and right resistance sections 17L, 17R of identical construction disposed side by side. Obviously, the resistance member 17 may have one-piece structure formed by a single piece of metal block.

As shown in FIG. 4, the protrusions 24 formed on the front surface of the flat plate-like base 23 are separated by a plurality of parallel spaced longitudinal grooves 34 a and a plurality of parallel spaced transverse grooves 34 b that form the labyrinthine central part or portion 34 of the vent passage 16. The longitudinal grooves 34 a are defined between the protrusions 24, and the transverse grooves 34 b are formed in the front surface of the base 23. Thus, the transverse grooves 34 b are made deeper than the longitudinal grooves 34 a such that a desired resistance can be produced when the motel metal advances along the central portion 34 of the vent passage 16. The transverse groove 34 b may have the same depth as the longitudinal grooves where appropriate.

As previously described, the resistance member 17 is removably mounted to the fixed mold member 11. Accordingly, by preparing two or more resistance members whose protrusions are different in number and size, it is possible to change the resistance members 17 as appropriate according to desired qualities of a die cast article or casing to be produced. More specifically, because a flow velocity of molten metal as the molten metal advances along the vent passage 16 is variable with the cross-sectional area of the vent passage 16, by changing the resistance members in an appropriate manner, it is readily possible to adjust the flow velocity of the molten metal at the central portion 34 of the vent passage 16 to the extent that residual air and/or gas in the die cavity is fully exhausted without being dragged into the molten metal, which would otherwise result in gas holes and the like in the die cast article or casting, thereby degrading the product qualities of the casting. Thus, castings with desired qualities can be obtained without requiring a long time for adjustment and preparation of the die casting mold.

Furthermore, by standardizing the size and shape of the bases 23 of the respective resistance members 17 as well as the size and shape of the retaining recesses 35 (FIG. 2) of the respective holders 27, it is possible to use one resistance member 17 in combination with plural different molds, or alternatively plural different resistance members can be used in combination with one mold. With this arrangement, enlargement in size of the die casting mold can be avoided and the maintenance cost of the die casting mold can be reduced.

As previously discussed, the protrusions 24 of the resistance member 17 are arranged in staggered relation to one another in both a longitudinal direction and a transverse direction of the vent passage 16 so as to define the labyrinthine vent passage part 34 extending between an inlet side and an outlet side of the vent passage 16. Accordingly, unsolidified molten metal, which may flash out from the die cavity 13 (FIG. 2) when residual air and/gas in the die cavity 13 is exhausted, will advance in a zigzag or meandering manner along the labyrinthine vent passage part 34, as indicated by arrows X shown in FIG. 5. During that time, since the molten metal strikes the protrusions and enters the transverse grooves 34 b, a flow velocity of the molten metal is sufficiently reduced to the extent that the molten metal is chilled by the resistance member 17 and the mating surface 26 of the movable mold member 12 and becomes solidified before it arrives at the downstream end of the vent passage where the exhaust valve (poppet valve) 18 is disposed.

A die casting process carried out by a die cast machine incorporating therein the die casing mold 10 of the foregoing construction will be described below with reference to FIGS. 6A to 6D.

As shown in FIG. 6A, the die cast machine operates to move the movable mold member 12 toward the fixed mold member 11 to dose the mold 10 with the die cavity 13 formed therein. The mold 10 is kept in this closed state with a predetermined clamping pressure. In this instance, the cylinder 15 is filled with molten metal 39. The exhaust passage 22 is connected to the exhaust ventilation device (not shown) disposed outside the mold 10. The exhaust ventilation device is normally driven to continue its exhausting operation while the die cast machine is operating.

Then, the plunger 14 is driven to force or change the molten metal 39 at a low speed into the mold cavity 13, as shown in FIG. 6B. In this instance, the exhaust valve 18 (FIG. 1) disposed at the downstream end of the vent passage 16 is opened so that residual air and/or gas in the die cavity is exhausted outside of the mold 10 successively through the vent passage 16 including the resistance member 17, the valve hole 21 and the exhaust passage 22, as indicated by the arrow “a” shown in FIG. 6B.

It may occur that the molten metal 39 is flashed from the die cavity 13 into the vent passage 16. However, by virtue of the labyrinthine vent passage part 34 (FIG. 5) formed between the protrusions 24 of the resistance member 17, it takes a relatively long time to fill the vent passage part 34 with the molten metal 39. This ensures that residual air and/or gas in the cavity 13 (including air and gases inside the molten metal 39) is fully exhausted outside of the mold 10. Thus, in synchronism with the low-speed charging of the molten metal 39 into the die cavity 13, the exhaust valve 18 (FIG. 1) is opened to allow for escape of residual air and/or gas in the die cavity 13 as well as air and/or gas in the molten metal 39 charged inside the die cavity 13. The opening timing of the exhaust valve 18 is determined on the basis of information obtained through trial runs, accumulated data, experiments, cycle time, and mold qualities.

Subsequently, the advancing speed of the plunger 14 is changed from the low speed to a high speed, whereupon the molten metal 39 remaining inside the cylinder 15 is charged at the high speed into the die cavity 13 so that the die cavity 13 is filled with the molten metal 39, as shown in FIG. 6C. The plunger speeds are determined through trial runs. At the same time the plunger speed is shifted up, the exhaust valve 18 (FIG. 1) is closed to block fluid communication between the vent passage 16 and the exhaust passage 22.

Then, the movable mold member 12 is moved backward away from the fixed mold member 11, and a die cast article or casting 41 is removed from the mold 10, as shown in FIG. 6D. A single cycle of operation of the die casting process has thus completed.

As thus far explained, the resistance member 17 including a plurality of discrete protrusions 24 (FIG. 2) is disposed in a vent passage 16 formed in a mating surface 26 of the fixed mold member 11 so as to resist or hinder smooth movement of molten metal to thereby reduce a flow velocity of the molten metal as the molten metal advances along the vent passage 16. The resistance member 17 is disposed inside the die casting mold 10 and hence does not enlarge the overall size of the mold 10. Furthermore, by virtue of a labyrinthine vent passage part 34 (FIG. 4) formed between the protrusions 24 of the resistance member 17, the velocity of the molten metal advancing along the labyrinthine vent passage part 34 is greatly reduced. This means that it take a relatively long time to fill such vent passage part 34 with the molten metal with the result that residual air and/or gas in the die cavity 13 (including air and/or gas in the molten metal) can be fully exhausted out of the mold 10. Additionally, the molten metal, as it advances along the labyrinthine vent passage part 34, is sufficiently chilled by the resistance member 17 and the mating surface 26 (FIG. 2) of the movable mold member 12 and becomes solidified before the molten metal arrives at a junction between the vent passage 16 and the valve hole 21 (FIG. 2).

In the illustrated embodiment, the resistance member 17 having a plurality of discrete protrusions 24 arranged in staggered relation to one another is incorporated in the fixed mold member 11 as a separate member structurally independent from the fixed mold member 11. The invention should by no means be limited to the illustrated arrangement but may include a modification in which the discrete protrusions 24 are formed integrally with the fixed mold member 11. In the latter case, since the resistance member 17 can be formed merely by machining the mating surface 26 of the fixed member 11, it is possible to produce the resistance member 17 at a reduced cost. The resistance member 17 may be incorporated in the movable mole member 12 in which instance the vent passage 16 is formed in the mating surface 26 of the movable mold member 12.

When the die casting mold 10 is dosed, the top surfaces 25 of the protrusions 24 of the resistance member 17 and the mating surface of the movable mold member are brought into contact with each other. In this instance, since the top surfaces 25 of the protrusions 24 are flat and hence can provide a relatively large contact area relative to the flat mating surface 26 of the movable mold member 12, the resistance member 17 can be held stably without causing deformation of the protrusions 24, which would otherwise occur due to a difference in the claming force applied to the fixed and movable mold members 11 and 12. Thus, during the die casting process, the cross-sectional area of the vent passage part 34 of the resistance member 17 remains substantially unchanged and gives no adverse effects on the qualities of die cast articles or castings.

INDUSTRIAL APPLICABILITY

With the arrangements so far described, the present invention can be used advantageously as a mold for synthetic resin molding processes. 

1. A die casting mold comprising: a fixed mold member; a movable mold member movable toward and away from the fixed mold member to define therebetween a die cavity when the die casting mold is closed; a vent passage formed in a mating surface of one of the fixed mold member and the movable mold member and extending in communication with the die cavity to allow for escape of residual air and/or gas from the die cavity when a molten metal is charged into the die cavity; and a resistance member disposed in the vent passage to reduce a flow velocity of the molten metal as the molten metal advances along the vent passage, wherein the resistance member comprises a plurality of discrete protrusions arranged in staggered relation to one another in both a longitudinal direction and a transverse direction of the vent passage so as to define therebetween a labyrinthine part extending between an inlet side and an outlet side of the vent passage.
 2. The die casting mold as claimed in claim 1, wherein the other of the fixed mold member and the movable mold member has a mating surface including a flat portion adapted for abutment with top surfaces of the protrusions.
 3. The die casting mold as claimed in claim 2, wherein the top surfaces of the protrusions are flat and engageable flatways with the flat mating surface portion of the other mold member.
 4. The die casting mold as claimed in claim 1, the labyrinthine part of the vent passage including a plurality of parallel spaced first grooves extending in the longitudinal direction of the vent passage and a plurality of parallel spaced second grooves extending in the transverse direction of the vent passage, the second grooves being deeper than the first grooves.
 5. The die-casting mold as claimed in claim 1, wherein the resistance member is formed by a separate member structurally independent from the one mold member and removably mounted to the one mold member, the resistance member including a flat plate-like base detachably mounted to the one mold member with the protrusions formed on one surface of the flat plate-like base.
 6. A chill vent structure for a die casting mold, comprising: a flat plate-like base; and a plurality of discrete protrusions formed on one surface of the flat plate-like base and arranged in staggered relation to one another so as to define therebetween a vent passage of labyrinthine structure.
 7. The chill vent structure as claimed in claim 6, wherein the protrusions have flat top surfaces.
 8. The chill vent structure as claimed in claim 6, wherein the vent passage includes a plurality of parallel spaced first grooves extending in a longitudinal direction of the vent passage and a plurality of parallel spaced second grooves extending in a transverse direction of the vent passage, the second grooves being deeper than the first grooves. 